Researchers shed light on mystery of why repellent DEET works to ward off insects

A study has shown how receptors and nerve cells in insect antennae react to the repellent.

AAP: University of Queensland, file photo

Researchers have discovered why one kind of insect repellent is effective, a discovery which could lead to a potential broad spectrum solution to bugs.

The compound dimethyltoluamide, also known as DEET, has been a successful insect repellent for more than six decades.

Scientists never knew exactly why, but a new study shows how receptors and nerve cells in insect antennae that react to the repellent.

Researchers at the University of California Riverside created a computer program to screen half a million compounds to predict new repellents.

From the thousands of compounds discovered they chose several hundred that were naturally occurring, before whittling those down to four that have strong effects on both mosquitoes and fruit flies.

Associate Professor Anandasankar Ray says the study, published in the journal Nature, successfully identified compounds that were not only safe but already appear in products fit for human consumption.

"What was absolutely critical for us was to try and quickly identify compounds that would be safe, and therefore have potential to go through trials for use with humans - compounds that were affordable, pleasant smelling and strong repellents," she said.

"These compounds, methylethylamade, ethyl anthranilate and butyl anthranilate are found in plum, in grapes and jasmine extract, they're also found in orange flower blossoms and a number of other natural sources.

"Just because they're natural doesn't necessarily always mean that they're safe, they are perhaps safer but not necessarily safe."

However Professor Ray says in this case, the compounds are approved by the Food and Drug Administration for addition to food, such as flavourings for chewing gum.

"Kool-Aid has some of these compounds, which I've heard gives it grape-like flavours, and they're approved as additives in fragrances."

Discovery could lead to affordable, broad spectrum repellent

Professor Ray says the findings are crucial for creating an insect repellent product affordable to the developing world.

"That has always been our key motivation, to try and find a substitute that is not only better for use in the developed world, but is also excellent and affordable in parts of the tropical world where disease transmission is prevalent," she said.

"DEET has no impact in control of disease in these areas because of the costs in these parts of the world, as well as the sticky inconvenience of applying it to every square inch of your body.

"We think some of these compounds we've found and some of the ones that are in our freezer at the moment could be key to being able to take repellent strategy to control malaria, dengue, flavivirus, West Nile virus and other insect transmitted diseases in tropical parts of the world."

Additionally, Professor Ray says the discovery could lead to a broad spectrum insect repellent.

"DEET receptor Ir40a is extremely well conserved across insects and not only is it found in mosquitoes and drosophila flies, this receptor is also present in a number of different insects that destroy crops and greens," she said.

"It is also found in other bugs that humans don't like, like lice and bed bugs.

"So we are designing a strategy to come up with a broad spectrum insect repellent that can work not only for protecting humans, agricultural animals or pets from disease transmitting insects and pesky insects, but perhaps also one day be useful to protect fields of grain or fruits in a tree from insects."